Satellite geodesy has become a powerful and reliable approach for investigating of geophysical processes, including tectonic, seismic, and volcanic activity. In seismotectonic research, the Global Navigation Satellite System (GNSS) provides precise estimates of plate motion parameters and offers valuable insights into present-day crustal deformation. The determination of Euler pole parameters and plate velocities represents a fundamental problem in global tectonics and a critical component of many geodynamic studies. This study aims to determine and analyze the parameters that characterize tectonic plate motion, specifically the rotation pole position (Φ, λ) and the angular rotation rate (Ω). The present-day kinematics of major tectonic plates are investigated using hundreds of geodetic observations provided by the Nevada Geodetic Laboratory (NGL) over the period 2000–2025. The analysis is based on GNSS station positions and velocities expressed in the International Terrestrial Reference Frame 2020 (ITRF2020). The estimation of Euler pole parameters for five major tectonic plates resulted in the following preliminary findings: for the African plate (𝜆𝐴𝑓=−81.97°±0.37; 𝜑𝐴𝑓=50.08°±0.14 and 𝛺𝐴𝑓=0.2665°𝑀𝑦𝑟⁄±0.0010);for the Eurasian plate (𝜆𝐸𝑢=−99.51°±0.98; 𝜑𝐸𝑢=54.61°±0.62 and 𝛺𝐸𝑢=0.2581°𝑀𝑦𝑟⁄±0.0016); for the North American plate (𝜆𝑁𝐴=−88.70°±0.32; 𝜑𝑁𝐴=−8.18°±0.42 and 𝛺𝑁𝐴=0.1863°𝑀𝑦𝑟⁄±0.0009 ); for South American plate (𝜆𝑆𝐴=−128.17°±0.92; 𝜑𝑆𝐴=−19.12°±0.35 and 𝛺𝑆𝐴=0.1178°𝑀𝑦𝑟⁄±0.0015) ; and for the Australian plate (𝜆𝐴𝑢=37.87°±0.22; 𝜑𝐴𝑢=32.84°±0.15 and 𝛺𝐴𝑢=0.6331°𝑀𝑦𝑟⁄±0.0007).The results were compared with the NNR-MORVEL56 plate motion model, providing key information for geodynamic modeling and insights into present-day tectonic behavior and seismic hazard.
Keywords
GNSS Stations; Tectonic Plates Velocities; Euler pole Parameters; ITRF2020.

How to cite: Allal, S. H., Hasni, K., and Dekkiche, H.: Recent Kinematics Analysis of Major Tectonic Plates from GNSS Positions and Velocities in the ITRF2020, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10128, https://doi.org/10.5194/egusphere-egu26-10128, 2026.

North-Eastern Italy is of particular interest in tectonics as it lies on the northernmost edge of the convergent margin between Eurasia and the Adria microplate, influencing regional deformation and seismicity. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to regional seismic hazard assessment.

Tunini et al. (2024) described the time series spanning two decades from GNSS stations located in north-eastern Italy and surrounding areas, as well as the resulting velocity field in the ITRF14 reference frame. The documented dataset was obtained by processing GPS observations with GAMIT/GLOBK software version 10.71. The time series, estimated using the same procedure, are collected daily and stored as part of a long-term monitoring project, with annual updates of velocity solutions computed.

In this study, we present a multi-constellation solution and evaluate the differences compared to the GPS-only solution. We also update the solution to the new implementation of the International Terrestrial Reference Frame (ITRF2020). We then analyse the impact of the new reference system on the characteristics of the time series and the velocities. We also include additional stations that have recently become available in the solution.

We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support (IscraC IsCd5_MGNSS20).

Reference:

Tunini, L., Magrin, A., Rossi, G., and Zuliani, D.: Global Navigation Satellite System (GNSS) time series and velocities about a slowly convergent margin processed on high-performance computing (HPC) clusters: products and robustness evaluation, Earth Syst. Sci. Data, 16, 1083–1106, https://doi.org/10.5194/essd-16-1083-2024, 2024.

How to cite: Magrin, A., Tunini, L., Zuliani, D., and Rossi, G.: Adria-Eurasia collision front: Multi constellation GNSS data Processing in ITRF2020 reference frame, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11657, https://doi.org/10.5194/egusphere-egu26-11657, 2026.

Ocean Bottom Pressure gauges (OBPs) are devices installed on the seafloor to continuously measure ocean bottom pressure. They are expected to detect vertical seafloor crustal deformation caused by transient tectonic events. However, OBP data contain pressure changes originating from various sources other than tectonic events, such as ocean tides, non-tidal fluctuations due to meteorological and oceanic variations, and instrumental drift. We need to remove these non-tectonic components to identify the pressure changes related to vertical crustal deformation. However, the timescale of non-tidal fluctuations (ocean noise) is similar to that of transient tectonic signals, such as slow slip events (SSEs), which makes it difficult to separate these components.

Otsuka et al. (2023) applied principal component analysis (PCA) to seafloor pressure data obtained by an OBP array to detect transient events, assuming that pressure changes due to transient events cause temporal fluctuations in the PCA results. To verify the performance of this method, they applied PCA to synthetic data and confirmed that the method can detect temporal changes in the composition of principal components (PCs). In the present study, we apply this method to OBP data obtained before the 2011 Tohoku earthquake, which includes transient events resulting from aseismic slip, as reported by Ito et al. (2013), to verify whether we can identify the event through temporal changes in the PCs decomposed from the OBP data. We performed PCA on de-tided OBP data covering about four months before the Tohoku earthquake using a short sliding time window, to examine temporal variations in the PCs.

Changes in the PCs were evaluated using the normalized inner product (NIP) of the eigenvector of each PC (Otsuka et al., 2023), which measures the difference in the direction of the vector. We expect the NIPs to be stable if the OBP data do not contain any transient events, whereas evident changes in the NIPs of more than one PC would occur when transient pressure variations are included in the data. In the present study, the NIPs of PC1 (the most significant component) and PC2 (the second most significant component) remained stable over time, whereas the NIPs of PC3 and PC4 began to decrease as the moving window (60-day length) approached late January 2011 and remained low for about 40 days. Based on a comprehensive analysis of seismic and geodetic data, including the same OBP data, Ito et al. (2013) reported that an SSE lasted for about 40 days from late January 2011. The NIP changes detected in the present study may correspond to pressure changes due to this transient event.

How to cite: Yamada, T., Hino, R., Kubota, T., Otsuka, H., and Ohta, Y.: An Attempt to Detect Transient Crustal Deformation from Ocean Bottom Pressure Gauge Data Using Principal Component Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3717, https://doi.org/10.5194/egusphere-egu26-3717, 2026.

Precise seafloor geodetic measurements are essential for understanding plate tectonics, earthquake cycles, and volcanic activity. Seafloor pressure gauges provide a key tool for monitoring vertical changes in the seafloor elevation. However, distinguishing millimeter-scale tectonic signals from instrumental drift and environmental noise remains a fundamental challenge in deep-ocean observing.

This presentation evaluates the performance and data integrity of self calibrating bottom pressure recorders (BPR) deployed by Ocean Networks Canada (ONC) offshore Vancouver Island. Instruments like the RBR BPRZero and the Sonardyne FETCH AZA utilize Ambient-Zero-Ambient (AZA) in-situ calibration mechanisms to quantify sensor drift. The AZA method involves switching a pressure gauge from ambient (seafloor) pressure to atmospheric pressure within the instrument's housing. By comparing this internal pressure reading to an accurate barometer also measuring internal pressure, the drift can be precisely determined and a calibration function applied.

A forensic analysis of the dataset reveals that, while the high-resolution pressure measurements capture true genuine environmental signals, they are also significantly contaminated by instrumental artifacts that are partially related to the measurement approach itself. In this study we report findings from preliminary deployments and discuss the methodological challenges encountered, proposing mitigation strategies for future applications.

How to cite: Schlesinger, A., Heesemann, M., Dexter, J., Leconte, J.-M., Davis, E., Sun, T., Kreimer, N., and Aghaei, O.: Assessing Data Integrity in Seafloor Geodesy: An Analysis of Self-Calibrating Pressure Data Collected by Ocean Networks Canada, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1585, https://doi.org/10.5194/egusphere-egu26-1585, 2026.

Continuous observations of seafloor water pressure, which enable detection of vertical seafloor motion, are an essential technique in seafloor geodetic observations. For such geodetic applications, observation instruments equipped with Digiquartz sensors manufactured by Paroscientific Ltd. are commonly used because of their extremely high accuracy, resolution, and stability. Downsizing of observation instruments are important for making dense network allowing detection of subtle crustal deformation; however, the relatively high power consumption of Digiquartz makes it difficult to downsize self-pop-up mobile observation systems.

Our group has used RBRduo3, temperature–pressure loggers as auxiliary instruments to monitor environmental conditions in other seafloor observations, such as seafloor acoustic ranging. Given that these products are compact, lightweight, and capable of easily acquiring continuous records over periods exceeding one year, we investigated their potential applicability to seafloor geodetic observations. To this end, we conducted parallel observations with ocean-bottom pressure recorders (OBPRs) equipped with high-precision Digiquartz sensors and RBR loggers.

Pressure records from RBR loggers exhibit large transient variations immediately after deployment on the seafloor, with amplitudes up to about an order of magnitude larger than the typical transients observed in Digiquartz sensors. However, except for approximately the first three days after installation, this behavior can be well approximated by a time-dependent function combining an exponential term and a linear term, and no other irregular fluctuations are observed.

Results from parallel observations at sites with water depths exceeding 5,000 m show that, aside from the initial post-deployment transients, pressure time series obtained by RBR loggers agree well with those from Digiquartz sensors. In contrast, at shallower sites with water depths less than about 2,000 m, the pressure time series from the two instruments differ substantially. The time series of the pressure differences closely resembles the temperature time series, suggesting that these discrepancies arise from insufficient temperature correction of the RBR pressure data.

Assuming that apparent pressure variations caused by temperature changes dominate the short-period components of the pressure fluctuations recorded by the RBR logger, we estimated a coefficient for temperature correction by minimizing the power of the fluctuations. Using this coefficient, we removed the temperature-correlated component over the entire frequency band. As a result, we obtained pressure time series that agree with those from the Digiquartz sensors within approximately 0.2 hPa in the parallel observations. This demonstrates that, with appropriate temperature correction, it is possible to obtain pressure variation data from RBR loggers that are comparable in quality to those from Digiquartz sensors.

By taking advantage of their compact size and low power consumption, RBR loggers could be applied as add-on instruments to ocean bottom seismometers and similar seafloor observation instruments, and are expected to contribute to an increased number of observation points in mobile seafloor observation networks.

How to cite: Hino, R., Suzuki, S., Sato, M., Yamada, T., and Ohta, Y.:  Quality assessment of seafloor pressure data from RBR loggers for applications to seafloor geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6150, https://doi.org/10.5194/egusphere-egu26-6150, 2026.

The Cascadia Subduction Zone (CSZ) is a convergent margin extending from Northern California to Northern Vancouver Island that is capable of creating M9+ earthquakes. Direct seafloor geodetic observations near the deformation front and the locked zone are required to constrain possible rupture scenarios. Until recently, observations of plate motion have been limited to land-based stations, which are insufficient to resolve the variability of potential rupture scenarios. Consequently, different model scenarios yield varied outcomes for hazard assessments and the development of effective mitigation strategies. Offshore Oregon and Washington (Central Cascadia), this critical data gap is being addressed by GNSS-Acoustic (GNSS-A) observations that recently provided seafloor geodetic evidence indicating near-full locking on the shallow megathrust (DeSanto et al., 2025).

To the north, offshore Vancouver Island, the Northern Cascadia Subduction Zone Observatory (NCSZO) project, primarily funded by the Canada Foundation for Innovation (CFI) and operated by Ocean Networks Canada (ONC), provides seafloor geodetic observations that will constrain model scenarios and offer the opportunity to observe along-strike variations. The NCSZO complements ONC’s NEPTUNE cabled seafloor observatory, which provides real-time data from seismometers, bottom pressure recorders, CORK borehole observatories, and other sensors relevant to seafloor geodesy. The NCSZO is composed of two main offshore components: a GNSS-Acoustic (GNSS-A) seafloor geodesy network with seven stations and a Deformation Front Laboratory providing pressure and tilt measurements across the deformation front. This presentation will provide an overview of the NCSZO and will highlight the first results from the GNSS-A stations, which consist of accurately located seafloor benchmarks. These benchmark locations are monitored via tens of thousands of acoustic interrogations during yearly surveys utilizing an autonomous Wave Glider.

Following the completion of a fourth observation campaign in 2025, we start to see meaningful results from several sites that provide constraints on the locking of the Juan de Fuca plate with the overriding North American plate. These first direct GNSS-A measurements in Northern Cascadia are a significant step towards improving the reliability of regional earthquake and tsunami hazard and mitigation models.

How to cite: Heesemann, M., Hutchinson, J., Sun, T., Wang, K., Davis, E., Bailly, N., Schlesinger, A., and Trenaman, F.: Near-Trench Seafloor Geodesy: GNSS-Acoustic Plate Motion Measurements at the Northern Cascadia Subduction Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13992, https://doi.org/10.5194/egusphere-egu26-13992, 2026.

 Ocean-bottom pressure (OBP) gauges are a key tool in seafloor geodesy, providing time-series observations of vertical seafloor motion by continuously recording pressure variations associated with changes in water depth. However, OBP time series contain multiple superimposed signals in addition to crustal deformation, including tides, instrumental drift, and non-tidal oceanic fluctuations driven by atmospheric and oceanic processes. In particular, non-tidal oceanographic fluctuations have time scales comparable to long-term crustal deformation, making it difficult to separate them and accurately estimate long-term seafloor deformation.

 Ocean-model-based corrections have been proposed to isolate and remove non-tidal oceanographic components, offering a physically based approach. However, model–observation mismatches can leave large residuals after correction, making it harder to identify deformation-related signals. As a fundamental step toward understanding these model–observation discrepancies, this study quantifies the physical processes controlling OBP variability using an ocean general circulation model named OFES2 (Sasaki et al., 2020), which does not assimilate oceanic observations.

 As a first step, we assess the extent to which OFES2 can account for the observed OBP variability by directly comparing modeled and observed time series. The modeled OBP is compared with observed OBP records from pressure gauges deployed off northeastern Japan. Our results show that OFES2 reproduces the seasonal cycle of the observed OBP time series to some extent, whereas agreement at periods of several days to about a month remains limited in both amplitude and phase.

 To investigate the physical processes controlling the modeled OBP variability, we decompose the modeled OBP into four components: atmospheric pressure loading, sea surface height variability, horizontal density advection, and vertical advection, and quantify the relative contribution of each component. The decomposition indicates that atmospheric pressure loading and sea surface height variability dominate the modeled OBP fluctuations, while horizontal density advection contributes to part of the seasonal variability. Moreover, correlation analyses using the time-derivative of the observed OBP and the decomposed pressure components reveal episodic enhancements in correlation with the horizontal density advection term, suggesting that its contribution can temporarily increase during specific periods.

 We will extend the analysis by comparing OFES2 with longer-term OBP observations and discussing in more detail the contributions of each component to seafloor pressure variability.

How to cite: Hagihara, T., Ohta, Y., Wang, S., Sasaki, Y., Hino, R., and Otsuka, H.: Process Decomposition of Ocean-Bottom Pressure Variability: What OFES2 Reproduces and Misses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8768, https://doi.org/10.5194/egusphere-egu26-8768, 2026.

The Cascadia subduction zone represents a seismic hazard to the Pacific Northwest region of North America, yet the state of fault locking near the deformation front, which could cause a devastating tsunami upon rupturing, remains poorly understood due to limited offshore observations along the subduction zone. In this study, we present the first seafloor geodetic measurements of the horizontal deformation rates on the accretionary prism from an array of four Global Navigation Satellite System-Acoustic (GNSS-Acoustic) sites surveyed from 2016-2022. These GNSS-Acoustic sites, despite resting on the North American plate, show velocities that are a significant fraction of the subducting Juan de Fuca plate velocity. In contrast, the continuous GNSS stations along the Oregon coast are moving at velocities <1 cm/yr relative to the North American Plate. Locking models constrained by these offshore velocities show that the subduction zone interface near the deformation front must be nearly locked offshore Oregon. To satisfy both the onshore and offshore geodetic observations, the locked zone must be relatively narrow and only minimal aseismic creep is permissible at the deformation front. These results suggest that appreciable elastic strain has accumulated near the deformation front, which elevates the potential for tsunamigenesis along this portion of the subduction zone.

How to cite: DeSanto, J., Schmidt, D., Zumberge, M., Sasagawa, G., and Chadwell, C. D.: Near full locking along the shallow megathrust of the Cascadia subdduction zone identified from seven years of GNSS-Acoustic observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11756, https://doi.org/10.5194/egusphere-egu26-11756, 2026.

The Main Marmara Fault (MMF) keeps unruptured since the last Marmara earthquake in 1766, while the most part of its extension along the North Anatolian Fault has released its strain through M7 class earthquakes progressively occurred during the last century. Revealing the coupling condition MMF is quite important because it controls magnitude of the next earthquake expected to be occurred.

Since the MMF is covered with sea water, acoustic ranging technique is required to monitor the fault behavior in geodetic measure. So far, two experiments were carried out to measure the creep rate of the MMF using acoustic extensometers; no significant creep at the west of Central High (Sakic et al., 2016), while nearly a half of the strain is released by creep at the Western High (Yamamoto et al., 2019). We further conducted the experiment at the west edge of Kumburgaz Basin to fill the spatial gap of the two experiments.

The experiment started from May 2017 installing five extensometers across a valley formed by MMF activity. Acoustic ranging was successfully operated between nine pairs out of ten combinations. The longest one is up to 3 km and the shortest one is just 0.5 km. The observed data were extracted remotely from a ship via acoustic communication while the measurement continues. We already extracted the data for nearly two years from the beginning to April 2019, just before the interruption due to COVID-19. Change rates in baseline length are evaluated using roundtrip times, which are converted into distance using sound speed corrected for in situ temperature of sea water. Combining change rates and crossing angle of their baselines with MMF, nearly 10-15 mm/yr of right-lateral creep is expected at the site.

Obtained result taken together the past experiments, the west half of MMF is partially creeping and the east half is rocked, which indicates that MMF still has a potential for over M7 earthquake. This distribution creep is consistent with electromagnetic imaging beneath the Sea of Marmara (Kaya-Eken et al., 2025). Our extensometers were still working at least the time of the Mw6.2 Marmara earthquake in April 2025, which occurred just beneath our site as a series of eastward progressive intermediate ruptures (Martinez-Garzon et al., 2025). We are expecting further data analysis after 2019.

How to cite: Kido, M., Takahashi, N., Yamamoto, Y., Özener, H., and Kaneda, Y.: Creep of the Main Marmara Fault at the west of the Kumburgaz Basin observed by acoustic extensometers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21272, https://doi.org/10.5194/egusphere-egu26-21272, 2026.

Deformation measurements from space-borne Interferometric Synthetic Aperture Radar (InSAR) resolve geodynamic signals at multiple spatial scales and are commonly integrated with ground-based measurements from the Global Navigation Satellite System (GNSS). The integration process requires accounting for reference frame discrepancies and measurement uncertainties. In this study, we propose a new approach, CoInSAR, which uses least squares collocation to transform InSAR displacement time series into the GNSS reference frame while correcting residual tropospheric errors from turbulent atmospheric effects that typically persist in InSAR data. In our approach, we construct the observation vector at each epoch from the displacement differences between GNSS and InSAR, which comprises the reference frame difference, measurement noise, and residual tropospheric errors. We represent the measurement noise via data variances and derive the stochastic model for residual tropospheric errors using an empirical covariance function estimated from InSAR displacements. By accounting for these stochastic components, we use least squares collocation to estimate the transformation parameter between the two reference frames, interpolate corrections for the residual tropospheric errors, and generate the integrated displacements. To assess the performance of our method, we applied CoInSAR to measure land subsidence in the San Joaquin Valley, California, and seismic deformation in Chile. Our results show high agreement between GNSS and CoInSAR time series and variance reduction in regions outside the GNSS network. Moreover, CoInSAR-based deformation estimates are not only consistent with physics-based models but also capture small-scale deformation features, highlighting CoInSAR’s potential to improve the modeling of geodynamic signals in regions with sparse GNSS coverage.

How to cite: Wang, C.-Y., Gómez, D., and Figueroa, M.: A least squares collocation approach to integrate InSAR and GNSS observations: CoInSAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12697, https://doi.org/10.5194/egusphere-egu26-12697, 2026.

While technologies such as satellite imaging are used in addition to seismic data for large magnitude earthquakes to confirm fault mechanisms, they are significantly less considered for the analysis of smaller sized events. However, constraining the nature of small to moderate magnitude seismic events with a sparse seismic network presents a significant challenge for monitoring agencies. The limitation in seismic coverage as well as low signal-to-noise levels measured in seismic data imply significant uncertainties in accurately estimating the source parameters (i.e., epicentral position, depth, magnitude and mechanism: earthquake, explosion, collapse). Quantifying and reducing these uncertainties becomes paramount, especially for the monitoring of shallow underground nuclear tests.

Here, we explore the advantages of combining seismic data and satellite borne Synthetic-Aperture-Radar-Interferometry (InSAR) techniques to recover the source parameters of superficial geophysical events using moment tensor techniques. We present the work we have undertaken for different types of shallow seismic events including earthquakes and collapses. From the acquisition of satellite images and seismic data to the comparison of the source solutions provided by both datasets, we explore the strengths and weaknesses of each approach that still need to be understood, and we propose joint approaches where possible. In the future, joint seismic-InSAR full moment tensor inversions may lead the way in the monitoring of regions with low seismic coverage.

How to cite: Guilhem Trilla, A., De Boever, H., Burgos, G., and Pinel-Puyssegur, B.: Improving Seismic Source Characterization of Moderate Magnitude Events at Regional Distance With Seismic and InSAR Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18873, https://doi.org/10.5194/egusphere-egu26-18873, 2026.

Spectacular natural hazards such as large earthquakes or volcanic eruptions are accompanied by smaller-amplitude processes that produce millimeter-scale ground deformation. Although subtle, these signals provide critical insight into the physical state of the system and their associated hazards. Interferometric Synthetic Aperture Radar (InSAR) offers the spatial resolution required to observe such deformation, but its exploitation over long time spans remains challenging due to centimeter-scale noise and systematic biases. Here, we demonstrate how state-of-the-art interferometric processing combined with a Kalman Filter–based Time Series analysis (KFTS) enables the extraction of millimeter-scale deformation from 10 years of Sentinel-1A/B data. 

We present two case studies: the Chaman fault system (Pakistan–Afghanistan) and the Natron rift (northern Tanzania) in the East African Rift. Careful step-by-step corrections of the interferograms include tropospheric and ionospheric corrections, azimuth shift compensation, and rigorous assessment of closure phase biases. Measurement uncertainties derived from coherence are propagated within the KFTS time-series inversion, allowing iterative estimation of phase evolution with associated uncertainties.

In the Chaman fault zone, we detect aseismic deformation characterized by fault creep rates of about 5 mm/yr, as well as a slow-slip event with ~1 cm of cumulative displacement resolved using combined ascending and descending geometries. In northern Tanzania, we resolve long-term rift opening of only a few millimeters per year between 2015 and 2025, consistent with GNSS campaign measurements. We further assess the potential of Independent Component Analysis (ICA) for InSAR signal separation and discuss current limitations imposed by residual noise and vegetation-related biases.

How to cite: Dalaison, M., Drique, L., Jolivet, R., Grandin, R., Pinel-Puysségur, B., Navarrete, I., Calais, E., and Olive, J.-A.: Resolving millimeter-scale tectonic deformation in decade-long InSAR time series : from long-term rifting to slow-slip events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17353, https://doi.org/10.5194/egusphere-egu26-17353, 2026.

Monitoring Volcanic Deformation Using InSAR: An Optimised InSAR Time-Series Approach for Seasonally Snow-Covered Volcanoes

¹Tianyuan Zhu*, ¹Juliet Biggs, ¹Alison Rust, ²Milan Lazecký, ³Loreto Cordova

¹School of Earth Sciences, University of Bristol, Bristol, United Kingdom

²COMET, School of Earth and Environment, University of Leeds, Leeds, United Kingdom

³Servicio Nacional de Geología y Minería (SERNAGEOMIN), Santiago, Chile
*tianyuan.zhu@bristol.ac.uk

Satellite-based Interferometric Synthetic Aperture Radar (InSAR) has been widely used for monitoring volcanic deformation, especially since Sentinel-1 launched in 2014, providing an unprecedented volume of routinely acquired, open-access data. Automated systems now continuously process interferograms and regularly update deformation time series, providing a valuable dataset for monitoring volcanoes globally. However, seasonal snow leads to coherence loss and subsequent unwrapping errors in interferograms, causing gaps in the network of the automated time-series analysis and reducing deformation accuracy. As ~41% of subaerial Holocene volcanoes exhibit seasonal snow cover (with snow persistence of 7-90%), optimising InSAR processing for seasonally snow-covered volcanoes would substantially improve monitoring active volcanoes, especially in high-latitude and high-altitude areas.  

In this study, we developed an optimised InSAR time-series processing workflow using MODIS 8-Day Snow Product, which has been successfully applied to Laguna del Maule (LdM), a caldera with strong seasonal snow cover in Chile (Snow Persistence=51%). At LdM, the default product from the LiCSBAS auto-processing system underestimates the average line-of-sight deformation by 28% at GNSS station MAU2 between 10/2014 and 06/2023. To improve the accuracy of time series, we adapt the LiCSBAS time-series processing strategy using the quantified relationship between MODIS 8-Day Snow Products and Sentinel-1 InSAR coherences. The optimised workflow, including an algorithm based on Graph Theory for network selection, reduced data requirements by ~90% and LiCSBAS processing time by ~80%, while improving the accuracy of the LiCSBAS-processed deformation to match GNSS observations.

Vegetation is another crucial factor in coherence loss, and cloud cover affects optical satellite data. Using MODIS products, we also show that over 50 of 484 seasonally snow-covered volcanoes have lower Normalized Difference Vegetation Index (NDVI) and cloud-obscured duration than LdM (NDVI=0.16; Cloud Duration=144 days), confirming that seasonal snow is their dominant source of coherence loss and MODIS products are applicable.

We applied our validated workflow to seasonally snow-covered volcanoes across a range of environments with different cloud and vegetation cover to produce a long-term deformation (2014–present) using Sentinel-1 data. The optimised workflow has implications for the accuracy and efficiency of global volcano monitoring, improving the quality of modelling and forecasting.

How to cite: Zhu, T.: Monitoring Volcanic Deformation Using InSAR: An Optimised InSAR Time-Series Approach for Seasonally Snow-Covered Volcanoes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14378, https://doi.org/10.5194/egusphere-egu26-14378, 2026.

Global Navigation Satellite System (GNSS) observations are widely used to monitor volcanic deformation through continuous measurements of surface displacements. Detecting subtle volcano-tectonic signals relies on stable and repeatable position estimates over long time periods, which can be difficult to achieve in complex atmospheric environments.

In geodetic GNSS processing, station coordinates are estimated jointly with tropospheric parameters, including zenith delays and, in many processing strategies, horizontal tropospheric gradients. These parameters are known to be coupled with the vertical component of the position and to reflect both large-scale and locally anisotropic atmospheric conditions. At volcanic summits, tropospheric variability is often enhanced by strong orographic effects, frequent cloud formation, intense precipitation, and, in tropical regions, persistently high atmospheric humidity.

In this study, we investigate the behaviour and temporal variability of tropospheric parameters estimated for GNSS stations installed near the summits of La Soufrière de Guadeloupe and Montagne Pelée in Martinique, two active volcanoes located in the tropical Lesser Antilles. The analysis focuses on zenith tropospheric delays, horizontal gradients, and their consistency over time, as well as on diagnostic indicators derived from GNSS phase residuals.

GNSS data are processed using two independent geodetic software packages, GINS and GipsyX, enabling a comparative assessment of tropospheric estimates and residual patterns obtained under different processing strategies. The GNSS-derived tropospheric parameters are examined in conjunction with observations from nearby meteorological stations and with the ECMWF ERA5 reanalysis, providing an external reference for the observed atmospheric variability.

This work presents an initial investigation of tropospheric modelling at volcanic summits in tropical environments. It discusses possible implications for the stability and interpretation of GNSS position time series used in volcanic deformation monitoring.

How to cite: Sakic, P. and Nahmani, S.: Investigation of the effect of tropospheric delay on the quality of GNSS time series in a volcanological context, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20324, https://doi.org/10.5194/egusphere-egu26-20324, 2026.

Steep relief and nearby ocean influenced weather patterns at Teide–Pico Viejo volcano create strong, elevation‑correlated tropospheric delays that can obscure millimetric ground motion in C‑band InSAR. We applied a robust workflow to isolate true deformation at Teide (2015–2025) by combining multi‑geometry Sentinel‑1 time series. Our pipeline integrates (i) ascending/descending TOPS stacks processed with SBAS method; (ii) numerical weather model corrections (e.g., ERA5‑based slant delays using PyAPS) to remove water‑vapor structure; and (iii) Common-mode filtering to minimize atmospheric residuals due a single deformation reference area (Mohammadnia et al., 2025). Finally, we recovered 3‑D deformation fields by combining information from 3 line‑of‑sight geometries. The atmospheric-corrected solutions substantially suppress topography‑correlated variance and reveal coherent, low‑amplitude deformation that otherwise would have been misinterpreted as larger magnitude volcanic deformation. The emergent pattern is dominated by slow, millimeters per year, deformation since 2022. Signals are superimposed with centimetric seasonal vertical signals. Our results demonstrate that rigorous atmospheric corrections are essential to recover sub-centimeter deformation spanning multiple years at high‑relief volcanoes to isolate magmatic-hydrothermal pressurization signals. 

References:
Mohammadnia, M., Yip, M.W., Webb, A.A.G., González, P.J. (2025) Spontaneous transient summit uplift at Taftan volcano (Makran subduction arc) imaged using an InSAR common-mode filtering method, Geophysical Research Letters, doi:10.1029/2025GL114853

Acknowledgements: We thank Spanish Agencia Estatal de Investigación project PID2022-139159NB-I00 (Volca-Motion) funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”. 

How to cite: Gonzalez, P. J., Mohammadnia, M., Boulesteix, T., Webb, A. A. G., and Charco, M.: Atmospherically corrected deformation at a prominent‑topography volcano: Teide-Pico Viejo volcano, Tenerife, Canary Islands (2015–2025), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10208, https://doi.org/10.5194/egusphere-egu26-10208, 2026.